The present invention relates to housewares and, more particularly, to electric mixers, blenders and food processors.
The electric blender such as disclosed, for example, in U.S. Pat. No. 3,156,278 has become an important element in many kitchens throughout the world. Such blenders typically include a bowl having a shaft centrally disposed in its bottom. One or more cutter blades, each having a plurality (typically four) of lobes, is rotated by a motor turning the shaft at high speed to comminute and/or blend materials in the bowl. In some such blenders, the bowl includes a generally clover-leaf shape to aid in mixing of the materials moving in rotary motion within the bowl.
U.S. Pat. No. 4,256,408, the disclosure of which is herein incorporated by reference, describes a dual blender having a bowl with a figure-eight cross section. A motor-driven shaft is centered in each of the lobes to improve the mixing action of the apparatus over that attained by a conventional single-shaft blender. In order to avoid conflict between blade tips without requiring synchronizing of the blade rotational positions, the device of this patent employs non-overlapping blades. Some of the references in the '408 patent also use a figure-eight container with dual rotating elements. These devices generally use overlapping rotating devices and thus require blade synchronization.
We have discovered that, although the apparatus of the referenced '408 patent does, indeed, improve mixing and/or comminution, a few problems with the design impair its performance. In particular, the use of a figure-eight bowl produces a cross section near the bottom which is substantially greater than that of a single-element device. A small amount of material to be treated makes a substantially shallower layer in the figure-eight bottom than in the circular bottom of prior-art device. As a consequence, a small amount of material in the bottom may not be reachable by the blades.
The '408 patent requires that its co-planar blades have their tip planes non-intersecting in order to avoid tip collision in a device without blade synchronization. Avoidance of tip collision is, of course, desirable and necessary. Product simplification also makes it desirable to avoid requirements for blade synchronization. However, we have found that interleaved blades do a better job of mixing, particularly of liquid or semi-liquid materials.